Alloys of magnesium and rare earths



United States Pat ALLOYS OF MAGNESIUM AND RARE EARTHS Rene Lucien, Paris, and Emile Tetart, Louvieduzen, France, assignors to Societe dlnventions Aeronautiaues et Mecaniques S. I. A. M., Fribourg, Switzerland, a corporation of Switzerland No Drawing. Application November 5, 1954, Serial No. 467,240

Claims priority, application France August 12, 1954 1 Claim. (Cl. 75168) The binary alloys of magnesium with rare earth metals are well known for their heat-resisting properties.

The study of the specific properties of the various rare earth metals has led the applicants to recognise thatamongst the binary alloys of magnesium and the rare earth metals the alloy of magnesium with didymium is that which has the best mechanical properties both in the cold state and in the hot state up to about 250 C. The content of didymium should be about 2 t 6% and preferably 4%.

In addition, the applicants have found that the mechanical properties of the alloy in the hot state depend, to a very great extent, on the percentage of lanthanum contained in the rare earth metals employed. Thus, for example, a content of 5 to 15% of lanthanum in the didymium used, which in the case of an alloy containing 4% of rare earth metals corresponds to a content of 0.2 to 0.6% of lanthanum in the alloy, appreciably increases its flow behavior.

Lanthanum is thus a favorable element, and it might be thought that its use at a high content would give a magnesium-lanthanum alloy having very good behavior under heat. Unfortunately, although the temperature only efiects the properties of the alloy to a small extent, the initial properties of this type of alloy are poor at ordinary temperatures.

A very useful compromise may be found in the use of a special mixture of rare earth metals which has, at the same time, a suflicient proportion of lanthanum to give the alloy good mechanical properties in the hot state, that is to say up to about 300? C., and of didymium to ensure adequate mechanical properties of the alloy when cold.

Researches made by the applicants have shown that alloys of magnesium with rare earth metals in which the rare earth metals are constituted by a mixture of lanthanum in a proportion of 20 to 75% with neodymium to 50%), praseodymium (5 to and samarium (0.5 to 17%) have excellent mechanical characteristics both in the hot and cold state.

In these alloys, the content of cerium, if there is any, should not exceed 10% by weight of the rare earth metals.

The proportion of the mixture of rare earth metals, as above defined, in the alloy is from 2 to 6%.

By way of example, very good results have been obtained, in particular with the mixtures of rare earth metals corresponding to the following composition:

It is necessary to make a distinction between the composition of the rare earth metals at the moment of their introduction into the magnesium and that obtained in the final alloy. In practice, the reducing action on salts of rare earth metals by magnesium varies in its effectiveness with the differentrare earth metals employed.

The effectiveness of reduction is, in general, highest in the case of neodymium, praseodymium and cerium. That of lanthanum is a little less and in the case of samarium, it is very low, and it is for this reason that, in an alloy in which the rare earth metals are present in the mixture introduced in the proportions given in the above example, their composition may vary between the limits indicated below for the content of rare earth metals obtained in the final alloy:

Percent Neodymium 40 to 65 Praseodymium 8 to 12 Samarium 0.5 Lanthanum 25 to 35 Cerium 2 to 10 The presence of zirconium in an alloy of the above composition increases its tensile strength in the cold state and its characteristics may then attain the following values:

Tensile strength --kg. per sq. mm-.. 23 to 25 Elasticity kg. per sq. mm 15 to 16 Elongation ..percent 5 to 6 Nevertheless, the flow characteristics are not improved by the introduction of zirconium. The invention also comprises certain special methods of thermal treatment to be applied to the binary alloys considered.

The homogenising treatment is carried out at about 570 C. At this temperature, neither deformation nor oxidation have been observed. Simple cooling in air is sufiicient afterwards. 'Then a tempering treatment at about 200 C. gives the optimum mechanical characteristics.

What we claim is:

An alloy of magnesium and rare earth metals consisting of 96% magnesium and 4% rare earth metals in the proportions of 25-35% lanthanum, 40-65% neodymium, 8-12% praseodymium, 0.5% samarium and 210% cerium.

References Cited in the file of this patent UNITED STATES PATENTS 2,302,968 McDonald Nov. 24, 1942 2,549,955 Iessup et a1 Apr. 24, 1951 2,569,477 Leontis Oct. 2, 1951 2,609,309 Meier Sept. 2, 1952 2,622,049 Hesse Dec. 16, 1952 FOREIGN PATENTS 491,182 Canada Mar. 10, 1953 OTHER REFERENCES Journal of Metals, vol. 1, pages 968-983, December 1949. 

